Sequence Grabber For Audio Content

ABSTRACT

An audio context object gathers multiple channels of audio data from an audio device and stores each channel of data separately in a ring buffer. Clients of the audio context can request any number of channels of data at any interval from the audio context. Multiple clients can share the same audio device. The ring buffer used by the audio context object stores the channels of audio data in a two-dimensional array such that each channel of audio data is stored in contiguous memory.

PRIORITY CLAIM; CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit as a Continuation of applicationSer. No. 11/158,482, filed Jun. 21, 2005 the entire contents of which ishereby incorporated by reference as if fully set forth herein, under 35U.S.C. §120. The applicant(s) hereby rescind any disclaimer of claimscope in the parent application(s) or the prosecution history thereofand advise the USPTO that the claims in this application may be broaderthan any claim in the parent application(s).

TECHNICAL FIELD

The present invention relates to multi-media digital data, and morespecifically, obtaining multiple channels of audio data for multipleclients.

BACKGROUND

Multimedia applications capture and playback various types of video andaudio data. For instance, a multimedia application may capture videoand/or audio data from various types of cameras, or from various devicesconnected to a computer. Audio, video and other types of media data maybe acquired from many different types of sources and devices. In orderto support capturing audio and video data from many different types ofdevices, a component-based architecture is frequently used.

In a component-based architecture, applications call certain functionsin an operating system component manager to perform high-leveloperations. For instance, a component-based multimedia application thatcreates movies may call a “record” function provided in the componentmanager to start recording from a device, a “pause” function provided inthe component manager to pause recording, etc. An application makesthese calls without regard to what type of device is being used. Byusing a component-based architecture, an application does not have toknow how to communicate directly with many different types of devices,instead it only communicates with the component manager.

One type of component that can be used to capture audio and video datais a “sequence grabber.” A sequence grabber component is used to “grab”,capture or obtain a sequence of digitized data, such as a sequence ofvideo images or a sequence of audio samples. For example, a sequencegrabber component can be used by an application to obtain video or audiodata for use in a movie that the application is creating, and save thedata as tracks in movie files.

An application instantiates a sequence grabber component to create thetop-level object through which the application controls how the data isobtained through high-level commands. Through the sequence grabbercomponent, a lower-level component called a “sequence grabber channelcomponent” is created to handle the acquisition of a channel of mediadata of a particular type. For example, an “audio” sequence grabberchannel component records a channel of audio or sound data, and a“video” sequence grabber channel component records a channel of videodata.

Current sequence grabber channel component implementations are limited.While different types of channels (e.g., one audio type channel and onevideo type channel) can simultaneously record from the same device, itis not possible to have two instantiations of an audio sequence grabberchannel component recording from a single device. In addition, whileknown audio sequence grabber channel components can record audio data instereo (i.e., audio data received from two channels), current audiosequence grabber channel components cannot grab more than two channelsof audio data. Furthermore, current audio sequence grabber channels arenot capable of sampling at a rate greater than 65 kHz.

Audio data today can be very large due to higher channel counts, highersampling rates and wider sample bit depths. In particular, many devicesgenerate multiple channels of audio data, such as 8 to 24 channels. Highend devices may generate even more channels of audio data. Newermultimedia applications, such as internet broadcast streaming, havecomplex audio recording requirements. For example, a multimediaapplication may need to be able to simultaneously record multiplechannels of audio data in various formats. A multi-channel audiosequence grabbing component is needed.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings and in whichlike reference numerals refer to similar elements and in which:

FIG. 1 is a block diagram of a system in which a sequence grabbercomponent is used in an application that creates a movie.

FIG. 2 is a block diagram of a system in which multiple instantiationsof audio sequence grabber channels communicate with an audio contextobject to grab multiple channels of audio data from multiple devices.

FIG. 3 illustrates an embodiment of a multi-channel audio context ringbuffer.

FIG. 4 illustrates an embodiment of a physical layout of the ring bufferof FIG. 3.

FIG. 5 is a block diagram illustrating a computer system upon whichembodiments of the invention may be implemented.

DETAILED DESCRIPTION

In the following description, for the purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present invention. It will be apparent, however,that the present invention may be practiced without these specificdetails. In other instances, well-known structures and devices are shownin block diagram form in order to avoid unnecessarily obscuring thepresent invention.

Sequence Grabber

A sequence grabber component implements the basic functionality of mediacapture for an application. Sequence grabber components allowapplications to obtain digitized data from external sources or deviceswithout communicating directly with any device drivers. An applicationinstantiates a sequence grabber component to create the object throughwhich it captures video or audio data from an external source. Onceinstantiated, the application communicates with the sequence grabberthrough high-level commands, such as “start recording”, “stoprecording”, “pause”, etc.

FIG. 1 illustrates how an example application that is creating a movie105 with at least two tracks 106, 107 uses a sequence grabber component110 to obtain media tracks for the movie. As shown in FIG. 1, in orderto handle specific media-related functions, the sequence grabber callson various sequence grabber channel components. Typically, differentsequence grabber channel components are used for different types ofmedia; for example, a ‘video’ sequence grabber channel component tocapture video data, a ‘sound’ sequence grabber channel component tocapture sound or audio data, etc. Although not shown in FIG. 1, othertypes of sequence grabber channel components may be used for other typesof media (e.g., text, Musical Instrument Digital Interface (MIDI),etc.).

In the example system shown in FIG. 1, video sequence grabber channelcomponent 120 records video data by communicating with video digitizercomponent 140, and sound sequence grabber channel component 130 recordsaudio data by communicating with sound input device component 150. Thevideo sequence grabber channel component 120 and the sound sequencegrabber channel component 130 present media data at regular intervals tothe sequence grabber 110, which may save the media data as tracks 106,107 in movie 105.

Sound input device component 150 is typically a low-level systemcomponent that is designed to communicate directly with sound inputhardware, such as audio device 160. This insulates all other componentsfrom having know anything about the current sound input hardware. Forexample, sound sequence grabber channel component 130 will simplyreceive a stream of bytes from sound input device component 150,irrespective of what type of device the audio device 160 is. An examplesound input device component may be the Sound Manager componentavailable from Apple Computer, Inc. of Cupertino, Calif. Alternatively,the example sound input device component may be a Core Audio HAL(Hardware Abstraction Layer) audio device driver, also available formApple. Other sound input device components can be used, or third-partydevelopers can write sound input device components to handlecommunication with particular devices.

Known sound sequence grabber channel components typically grab sequencesof audio samples from the first, second or the first and second channelsof an audio recording device, regardless of the number of audio channelsit supports at the driver level. They cannot record from multipledevices or record more than stereo (i.e., first two channels) from adevice that generates multiple channels. If audio device 160 is amodular digital multitrack device, such as an 8-channel ADAT deck, forexample, sound sequence grabber channel 130 can only grab, at most, twochannels of the eight channels produced by the ADAT deck.

Furthermore, multiple instantiations of sound sequence grabber channelcomponents cause errors, and therefore cannot be used to recordadditional channels. The techniques disclosed herein overcome theselimitations and provide multi-channel high resolution audio capturecapability.

FIG. 2 illustrates how a sequence grabber channel component implementedusing the techniques disclosed herein can be used to capture multiplechannels of audio data. In order to differentiate this sequence grabberchannel component from the sound sequence grabber channel component ofFIG. 1, the sequence grabber channel component implemented usingtechniques disclosed herein is called “Audio Sequence Grabber Channel”in FIG. 2, and will be abbreviated as “Audio SGChannel” herein.

Unlike sound sequence grabber channel components, multipleinstantiations of Audio SGChannel components are possible, asillustrated in FIG. 2 by Audio SGChannels 221, 222, 223 and 224.Multiple instantiations of Audio SGChannels allow an application to grabmultiple channels of audio data at the same time. For example, sequencegrabber 110 can use the four instantiations of Audio SGChannel of FIG. 2to record data for four separate audio tracks in a movie. FIG. 2illustrates only one example embodiment, and more or fewer AudioSGChannels are possible.

As shown in FIG. 2, the source to each Audio SGChannel is independent ofany other Audio SGChannel. This allows for a great deal of flexibilityin capturing and using tracks of audio. For example, a user can capturemultiple channels of audio from the same device, as shown by AudioSGChannels 223 and 224, and use the channels as multiple tracks in amovie. As another example, a user can capture multiple channels of audiofrom different devices to use as tracks in a movie. Many configurationsand uses will be apparent to those skilled in the art.

Significantly, in one embodiment the device layer that an AudioSGChannel communicates with is abstracted into an “audio context”object. Each Audio SGChannel grabs sequences of audio data from audiodevices 160, 260 and 261 through audio contexts 291, 292 and 293,respectively. Each audio context 291, 292, 293 provides a commoninterface for audio data coming from an input audio device, such thatthe audio context acts as if it is the input audio device component toeach of the Audio SGChannels.

Each per-device audio context may be shared among multiple clients. Forexample, audio context 293, associated with device 261, is shared byAudio SGChannels 223 and 224.

In one embodiment, in order to support a large number of audio devices,audio context 291, 292, 293 may receive audio data from different typesof audio input device components. For example, input device component150 may be Sound Manager Sound Input Component from Apple Computer,Inc., input device component 251 may be the CoreAudio HAL drivercomponent available in MAC OS X from Apple Computer, Inc., and inputdevice component 252 may be a DirectSound Application ProgrammingInterface (API) device from Microsoft, Inc., of Redmond, Wash. FIG. 2 ismerely an example, and many configurations are possible.

In the example shown in FIG. 2, Device A 160 may be an older devicewhich is only supported by Sound Manager, Device B 260 may be a devicefor which higher resolution CoreAudio support is provided, and Device C261 may be a device for which only Direct Sound support is provided.Furthermore, hardware-specific audio input device components may bedeveloped to communicate with specific devices. Because audio contextcan communicate with multiple audio input device components, AudioSGChannels are able to grab data from any type of device as long as itis supported by at least one audio input device component.

By having audio contexts 291, 292 and 293, Audio SGChannels can share acommon input device without interfering with each other. For example, asshown in FIG. 2, audio context 293 is shared by Audio SGChannels 223 and224. As a client of audio context, an Audio SGChannel does not need toknow what type of device input is coming from, which audio input devicecomponent is being used to communicate with the device or even whetherother instantiations of Audio SGChannels might be receiving data fromthe same device. For example, Audio SGChannels 223 and 224 may both begrabbing sequences of audio samples from Audio Device C (261) throughaudio context 293. Multiple instantiations of Audio SGChannel mayrequest data from the same input device, or they may request data fromdifferent input devices. In addition, different instantiations of AudioSGChannel may request the same channels from a device, or they canrequest different channels.

In order to allow multiple instantiations of Audio SGChannel components,in one embodiment each Audio SGChannel creates its own audio contextreference. Each connection from an Audio SGChannel client to the audiocontext is identified with a different connection identifier (“id”),even though different Audio SGChannels may ultimately be communicatingwith the same device. Separate connection ids (id) 281, 282, 283 and 284are shown in FIG. 2 for Audio SGChannels 221, 222, 223 and 224,respectively.

An audio sequence grabber channel component that can record multiplechannels of audio is useful in many situations. For example, suppose acomputer is set up with three 8-channel ADAT decks, thereby providing atotal potential input of 24 channels. In one embodiment, a first AudioSGChannel grabs audio data from the first deck, a second Audio SGChannelgrabs data from the second deck, and a third Audio SGChannel grabs datafrom the third deck. Sequence grabber component 110 can gather data fromthe three devices through the multiple instantiations of AudioSGChannel, and write the audio from different devices to the same moviefile. Alternatively, the audio can be used in separate movie files. Manyvariations are possible.

Each audio context receives input audio data from an audio input devicecomponent and places the data in a buffer. For example, audio context291 includes ring buffer 291, and audio data from input device component150 is placed in this ring buffer. Specific ring buffer techniques thatcan be used are discussed in detail below. As discussed in more detailsbelow, the audio data is placed in the ring buffer of an audio contextafter being de-interleaved, if necessary, and converted to 32-bitfloating point, if necessary.

Audio input device components 150, 251, 252 may provide multiplechannels of audio data to audio context as either interleaved audiodata, or de-interleaved channels of audio data. For example, FIG. 2illustrates that audio input device 150 delivers data as interleaveddata (171), and audio input device 252 delivers data alreadyde-interleaved (172). Audio context can handle either case, so thatdifferent kinds of audio input device components can be used with anaudio context. If an audio input device component provides data to audiocontext in de-interleaved format, audio context stores each channel ofdata separately. If the input audio data from an audio input device isinterleaved, audio context de-interleaves the data before storing eachchannel of data separately in the buffer. Either way, all channels ofaudio data from the input audio device are stored separately in the ringbuffer. As audio context stores the data de-interleaved, Audio SGChannelclients do not need to de-interleave audio data grabbed from audiocontext, whether the audio data was originally interleaved or not.

Audio context queues all audio data coming from the input devicecomponents. However, Audi SGChannel clients do not always have to graball channels gathered and stored by audio context. Audio SGChannels canrequest any subset of channels available from the device associated withthe audio context. In addition, Audio SGChannels can request channels inany order, such that data sent to an Audio SGChannel may be sent in adifferent order than it was received by audio context. Audio SGChannelscan even request multiple copies of the same channel, if desired.

For example, Audio Device C 261 may be a device that produces 8 channelsof audio data. Audio context 273 will de-interleave the data, ifnecessary, as it arrives from the input device component 252, and storethe de-interleaved data in audio context 273's ring buffer 293. Supposean application needs the first and second channels for a first track ina movie, and the third and fourth channels for a second track in amovie. In this example, two instantiations 223 and 224 of AudioSGChannel in FIG. 2 may be created by the application, one for eachtrack. Audio SGChannel 223 connects to audio context 273 with connectionid 283 and requests channels 1 and 2. Audio SGChannel 224 connects toaudio context 273 with connection id 284 and requests channels 3 and 4.Each Audio SGChannel client can selectively read, or receive from audiocontext 273, only the channels it wants from audio context ring buffer293.

In addition, in one embodiment, Audio SGChannels can request a channelof silence in addition to (or instead of) selected channels from anaudio input device. For example, if an Audio SGChannel needs to create astream of six channels for an application, but the audio input deviceonly produces four, this feature can be used to add two channels ofsilence to the four channels produced by the audio device to create a6-channel stream.

In the context of internet broadcasting, multiple instantiations ofAudio SGChannels are useful to obtain the same audio data in differentformats. For example, suppose an input device provides audio in 5.1surround sound, and an application is developed to re-broadcast theaudio data over the internet. Real-time re-broadcasting of 5.1 channelaudio data would generally not be possible over the internet due tobandwidth restrictions as 5.1 channel data audio data is very large.

In this example, three instantiations of Audio SGChannel can be used toprovide three different streams of audio data recorded at different datarates and compression, such that each can be re-broadcast asappropriate. For example, a first Audio SGChannel can grab all 5.1channel data from the audio context associated with the input device, asecond Audio SGChannel can grab the same data from the audio context ascompressed Advanced Audio Coding (AAC) data, and a third Audio SGChannelcan grab the data as a low bitrate stream of mixed down stereo sound(i.e., two channels). The audio data grabbed by the second AudioSGChannel is useful for re-broadcasting the data over broadbandconnections, while the audio data grabbed by the third Audio SGChannelis useful for re-broadcasting over slower connections. The applicationcan use these three Audio SGChannels to capture the audio data forre-broadcasting in three (or more) formats, so that the re-broadcastingapplication can support a variety of client connection speeds. The audiodevice does not need to change operation in order for an application tomake a multi-data rate movie that uses the same audio data as separatetracks stored at different data rates and different compressions. Theaudio input device simply plays what it has, and the application,through use of multiple Audio SGChannels and audio context, can use theinput audio data in any format.

Some audio input devices only allow one client at a time. The audio datafrom these “exclusive access” devices cannot be shared by multipleclients. However, since audio context provides a “wrapper” for the audioinput device, and can provide audio data to multiple clients through asingle ring buffer, clients can effectively share an exclusive accessdevice in one embodiment.

Using these disclosed techniques, multiple Audio SGChannels can shareaudio data from a common device. In addition, Audio SGChannels can grabany desired channel valiance, as Audio SGChannel clients are notrequired to gather data from all channels, even though audio contextreceives, de-interleaves and stores data from all channels. Furthermore,it is possible to grab data from multiple devices using multiple AudioSGChannels and store the audio data from separate devices as tracks inthe same movie.

In one embodiment, the audio context wraps a device for both input andoutput. Thus, if an Audio SGChannel wishes to play a real-time previewof the data being captured, it may do so using the same audio contextinterface. It may preview the data to the same device from which it wascaptured, or to a different output device. Multiple Audio SGChannels canshare common output device audio contexts just as they can share inputdevice contexts, so audio from different sources may be previewed onto acommon playback device. Mixing to the output device's channel valenceand speaker layout is performed automatically by the audio context.

Ring Buffer

The audio context ring buffer is used to store data received from anaudio device, while simultaneously allowing one or more Audio SGChannelclients to read from it. For example, in FIG. 2, ring buffer 293 ofaudio context 273 is accessed by Audio SGChannel clients 223 and 224.

A “ring buffer” is generally a circular queue primarily used fortransmitting data between asynchronous processes, and is especiallyuseful for applications that transfer audio data. Typically, a ringbuffer is an array wherein each block of new data coming into the bufferis written right after the previous block, with wraparound to thebeginning when the end of the buffer is reached. Processing of the datain a ring buffer takes place the same way, wrapping around to thebeginning when the end of the buffer is reached. “Head” and “tail”position pointers are maintained so that the processing never goes pastthe end of the new data. Data is inserted at the buffer's back end(tail) and removed from the front end (head).

FIG. 3 illustrates how a ring buffer for an audio context object isimplemented in one embodiment of the present invention. The example ringbuffer 310 shown in FIG. 3 illustrates a simple ring buffer containingten ring buffer elements (RE1-RE10), however any number of ring elementscan be used.

As shown in FIG. 3, at a high level, the ring buffer is a circularlinked list, with the last ring element RE10 (312) pointing back to thefirst ring element RE1 (311). Typically, each ring buffer element isintended to receive a “push” of audio data from an audio input devicecomponent.

In one embodiment, audio context calculates the number of ring elementsin the ring buffer as it allocates memory for the ring buffer. In oneembodiment, audio context determines the number of ring elements throughuse of a parameter or configuration variable that stores the totalbuffer time, and by querying the audio device to determine howfrequently chunks of audio data will be pushed to audio context. Forexample, suppose ring buffer 310 is intended to store 1 second of audiodata coming from a 4-channel device. In this example, the audio isdelivered in 1/10 of a second size chunks. In this example, it can beeasily determined that a 10 ring element ring buffer is needed to store1 second of data in 1/10 second chunks. Ring buffers containing more orfewer ring elements are of course possible. Other methods may be used todetermine how many ring elements to use in the audio context ringbuffer.

As shown by section 315 of ring element RE 1, the audio data received bythat ring element is separated by channel and each channel is storedseparately, in this example into 4 separate buffers for the 4 channels.Although the ring buffer 310 in FIG. 3 shows the separate channels beingstored within the ring elements, in one embodiment, each ring elementcontains pointers to each channel of data, and the channels of audiodata are stored separately from the ring elements.

Table 330 in FIG. 3 illustrates the ring buffer 310 as a conceptualtwo-dimensional table or array of de-interleaved audio samples from theexample 4-channel audio device. As shown, each push of data is stored ina row of the table. The data stored in each row of the table isseparated by channel, and stored in separate columns in the table. Forexample, suppose the data received in the first push is represented as“ABCD”, where “A” represents channel 1 data, “B” represents channel 2data, etc. As shown in table 330, each channel's data is stored inseparate columns in row RE1.

When the next push of audio data is received, it is separated by channeland stored in the appropriate corresponding column of row RE2. Forexample, if the second push of data is represented by “EFGH”, with “E”representing channel 1 data, etc., the push is stored in row RE2. Asfurther pushes of data come in, they are de-interleaved and added to thetable accordingly. Table 330 illustrates a time when 4 pushes of datarepresented by “ABCD”, “EFGH”, “IJKL” and “MNOP”, corresponding to the 4channels of data for each push, have been received and stored. When thetable is full, it will start over with the next push of data overwritingany data in row RE1, and so forth.

At the beginning, the tail and the head for each SGChannel client pointsto RE1. As the audio context is associated with one device, it onlyneeds to keep track of one “tail” as it only has one writer, i.e. theaudio input device component. However, as an audio context can havemultiple readers (Audio SGChannel clients), and the readers can pulldifferent numbers and amounts of samples out of the audio contextsimultaneously, the audio context must track a separate ring buffer“head” for each Audio SGChannel client. In one embodiment, the audiocontext keeps a data structure for each SGChannel client with which itis associated. Within each data structure, it keeps track of thatparticular client's read element and offset within that element. Thus atany given time, the audio context is able to determine how many samplesare available for any given SGChannel client as it keeps track of howmuch any given client has already consumed.

With each push, the tail is moved to the next row, and the head for anAudio SGChannel client remains pointing to RE1 until data is read bythat Audio SGChannel client. Suppose after two pushes, a first AudioSGChannel client requests all channel 1 and channel 2 data. At thispoint, the tail points to RE3, as this is the next row to which a pushof data will be added, and the head for the first Audio SGChannel clientpoints to RE1, as no data has yet been read. Audio context can deliverthe requested data by simply reading the Channel 1 and Channel 2 columnsfrom the first Audio SGChannel's head (RE1) to the tail (RE3) in order.In this example, the sequence of data represented by AEBF will bereceived by the first Audio SGChannel client. If the first AudioSGChannel client had requested Channel 2, then Channel 1, the sequenceof data represented by “BFAE” would instead be received by the firstAudio SGChannel client.

Clients can request data in any size chunks, and do not have to requestdata in the size of the push in which it is delivered to audio context.Clients can request more or less data because no de-interleaving isnecessary as the data has already been de-interleaved. Audio contextsimply delivers the amount of data in the buffer at the time of therequest.

Each Audio SGChannel has its own ring buffer head, so that each AudioSGChannel can receive the amount of data that it wants withoutinterfering with other Audio SGChannel clients. As mentioned above, theaudio context keeps track of each Audio SGChannel's read element andcurrent offset within that element. In one embodiment, Audio SGChannelclients pull out data by querying the audio context for a particularproperty in an API call. The audio context calculates the number ofavailable frames for the particular Audio SGChannel client making therequest, then the client pulls out that number of frames (samples) ofaudio data from audio context by calling another API function.

Using the example above, after reading the first two rows of data forChannel 1 and Channel 2, both the tail and the head for the first AudioSGChannel will point to RE3. Suppose the next two pushes of data are nowreceived by the ring buffer, represented by “IJKL” and “MNOP” in rowsRE3 and RE4, for channels 1-4 respectively. With the pushes, the tailwill move to RE5, and the head for the first Audio SGChannel clientremains at RE3. As described above, the first Audio SGChannel hasalready received Channel 1 and Channel 2 data for the first two pushes(rows) of data. When another request is received from the first AudioSGChannel, it will read data from the Channel 1 and Channel 2 columnsfrom the head to the tail, i.e., rows RE3 and RE4. In this example, thedata represented by “IMJN” will be received by the first Audio SGChannelclient.

However, suppose a second Audio SGChannel client, which requests onlyChannel 1, now wants to receive the Channel 1 data. After 4 pushes, thetail has moved to RE5, but since no data has been read for this AudioSGChannel client yet, the head for this Audio SGChannel still points toRE1. The Audio SGChannel will receive the first four rows (RE1-RE4) ofdata for the Channel 1 column in a single request in this example. Inthis example, the second Audio SGChannel client receives the datarepresented by “AEIM.”

As illustrated, Audio SGChannel clients can request data for any numberof channels available in the ring buffer, and can also request differentamounts of data in each request. The ability to request and receivevarying amounts of data is important in many situations. For example, ifa client is performing other functions, such as heavily processing theincoming audio data, it may not be possible to request and receive dataas frequently as it is pushed. The audio context for this client maygather up several pushes of data before the client requests and receivesthe data. However, another client may be associated with an applicationthat is capable of receiving audio pushes in real-time, and will requestand receive the selected channels of each push as it comes in.

An advantage of using a 2-dimensional array to implement a ring bufferfor multi-channel data is that the data can be stored and readsequentially by channel. That is, each column of the table is stored asa contiguous block. This enables a client to receive multiple pushes ofdata for that Channel with a single read. For example, in the example ofFIG. 3, Channel 1 data is stored as AEIM in a single contiguous block.This enables any size of request to be performed with only a single readof the buffer—the data is not fragmented throughout the buffer. Clientscan efficiently grab larger chunks of data on a less frequent basis, ifneeded. This is different from other ring buffers that store datadirectly in the ring buffer elements, or where each ring element isassociated with a separate buffer. In these cases, multiple reads ofseparate buffers associated with different ring elements may be neededin order to fulfill a request.

There are many ways of implementing the 2-dimensional table 330. FIG. 4illustrates one embodiment of a physical structure for the table. Asshown in FIG. 4, data structure 410 is used to store the entire ringbuffer 310. In this example, memory is allocated for the ring bufferstarting at memory location 0x100. The first ring element RE1 is storedstarting at this location, and is typically accessed by a pointer. Whenmemory at this address is accessed, it is interpreted to be a datastructure that holds ring element data. For example RE1 may be a datastructure that contains various information such as timestamps, audiopush identification information, such as a seed counter, audio sampleoffset information, number of samples or frames contained in a buffer, apointer to the next ring element, etc. Various types of information thatcan be stored will be apparent to those skilled in the art.

Each ring element is stored at a particular location in the datastructure. Each ring element contains a pointer to the next ringelement, and the last ring element contains a pointer to the first ringelement. In the example of FIG. 4, the “next” pointer 411 for RE1 may bedetermined by using the start address of RE+the byte size of RE1. Thiswill point to the start of RE2. Other techniques for implementing thedata structure and calculating the locations of ring elements will beapparent to those skilled in the art.

In addition, in one embodiment each ring element may contain one or moreoffsets that can be used to determine a location of the channel data forthat ring element, as shown by offset 415. Offsets will be discussed inmore detail below.

In one embodiment, ring buffer data structure 410 also contains a BufferList, shown as BL 440. The Buffer List is a variable length structureholding pointers to the starting point of each channel's actual data.The Buffer List is used in conjunction with the offsets in the ringelements to determine where in each channel's buffer the portion of datathat corresponds to that ring element is stored. In this example, theBuffer List may have a pointer to memory location 0x1000 for Channel 1,memory location 0x101000 for Channel 2, etc.

For example, suppose one second of data will have 100,000 bytes. Eachpush of data ( 1/10 second) will deliver 10,000 bytes. In this example,the offsets for each ring element can be determined as:

$\begin{matrix}{{{RE}\; 1.{offset}} = 0} \\{{{RE}\; 2.{offset}} = 10000} \\{{{RE}\; 3.{offset}} = 20000} \\\ldots \\{{{RE}\; 10\mspace{14mu} {offset}} = 90000}\end{matrix}$

When the first push of 10,000 bytes arrives at audio context, it isde-interleaved (if necessary), and Channel 1's data is written toChannel 1's start address (found in the Buffer List to be0x1000)+RE1.offset; Channel 2's data is written to Channel 2's startaddress (0x101000)+RE1.offset, etc. In this example, RE1.offset is 0, sothe data is stored at the start of each Channel's buffer. For example,Channel 1's data for ring element RE1, represented by “A”, is stored atlocation 0x1000, and Channel 2's data for ring element RE1, representedby “B” is stored at 0x101000.

When the second push of 10,000 bytes arrives, it is de-interleaved, andChannel 1's data for ring element RE2, represented by “E”, is written toChannel 1's start address+RE2.offset. In this example, the datarepresented by “E” is written to 0x11000. (0x1000+10000=0x11000).Channel 2's data, represented by “F”, is written to Channel 2's startaddress+RE2.offset, or (0x101000+10000) 0x111000. In this manner, eachchannel's data is stored as a separate contiguous block.

Other implementations of the 2-dimensional array 330 are possiblewithout using the physical structure illustrated in FIG. 4. In addition,while described in the context of a ring buffer for an audio contextobject, the multi-channel ring buffer techniques disclosed herein can beused in other applications, such as an application that plays multiplechannels of audio data.

Through a ring buffer created using the techniques described herein,audio context can deliver any amount of data at any time for any client.

Hardware Overview

FIG. 5 is a block diagram that illustrates a computer system 500 uponwhich an embodiment of the invention may be implemented. Computer system500 includes a bus 502 or other communication mechanism forcommunicating information, and a processor 504 coupled with bus 502 forprocessing information. Computer system 500 also includes a main memory506, such as a random access memory (RAM) or other dynamic storagedevice, coupled to bus 502 for storing information and instructions tobe executed by processor 504. Main memory 506 also may be used forstoring temporary variables or other intermediate information duringexecution of instructions to be executed by processor 504. Computersystem 500 further includes a read only memory (ROM) 508 or other staticstorage device coupled to bus 502 for storing static information andinstructions for processor 504. A storage device 510, such as a magneticdisk or optical disk, is provided and coupled to bus 502 for storinginformation and instructions.

Computer system 500 may be coupled via bus 502 to a display 512, such asa cathode ray tube (CRT), for displaying information to a computer user.An input device 514, including alphanumeric and other keys, is coupledto bus 502 for communicating information and command selections toprocessor 504. Another type of user input device is cursor control 516,such as a mouse, a trackball, or cursor direction keys for communicatingdirection information and command selections to processor 504 and forcontrolling cursor movement on display 512. This input device typicallyhas two degrees of freedom in two axes, a first axis (e.g., x) and asecond axis (e.g., y), that allows the device to specify positions in aplane.

The invention is related to the use of computer system 500 forimplementing the techniques described herein. According to oneembodiment of the invention, those techniques are performed by computersystem 500 in response to processor 504 executing one or more sequencesof one or more instructions contained in main memory 506. Suchinstructions may be read into main memory 506 from anothermachine-readable medium, such as storage device 510. Execution of thesequences of instructions contained in main memory 506 causes processor504 to perform the process steps described herein. In alternativeembodiments, hard-wired circuitry may be used in place of or incombination with software instructions to implement the invention. Thus,embodiments of the invention are not limited to any specific combinationof hardware circuitry and software.

The term “machine-readable medium” as used herein refers to any mediumthat participates in providing data that causes a machine to operationin a specific fashion. In an embodiment implemented using computersystem 500, various machine-readable media are involved, for example, inproviding instructions to processor 504 for execution. Such a medium maytake many forms, including but not limited to, non-volatile media,volatile media, and transmission media. Non-volatile media includes, forexample, optical or magnetic disks, such as storage device 510. Volatilemedia includes dynamic memory, such as main memory 506. Transmissionmedia includes coaxial cables, copper wire and fiber optics, includingthe wires that comprise bus 502. Transmission media can also take theform of acoustic or light waves, such as those generated duringradio-wave and infra-red data communications.

Common forms of machine-readable media include, for example, a floppydisk, a flexible disk, hard disk, magnetic tape, or any other magneticmedium, a CD-ROM, any other optical medium, punchcards, papertape, anyother physical medium with patterns of holes, a RAM, a PROM, and EPROM,a FLASH-EPROM, any other memory chip or cartridge, a carrier wave asdescribed hereinafter, or any other medium from which a computer canread.

Various forms of machine-readable media may be involved in carrying oneor more sequences of one or more instructions to processor 504 forexecution. For example, the instructions may initially be carried on amagnetic disk of a remote computer. The remote computer can load theinstructions into its dynamic memory and send the instructions over atelephone line using a modem. A modem local to computer system 500 canreceive the data on the telephone line and use an infra-red transmitterto convert the data to an infra-red signal. An infra-red detector canreceive the data carried in the infra-red signal and appropriatecircuitry can place the data on bus 502. Bus 502 carries the data tomain memory 506, from which processor 504 retrieves and executes theinstructions. The instructions received by main memory 506 mayoptionally be stored on storage device 510 either before or afterexecution by processor 504.

Computer system 500 also includes a communication interface 518 coupledto bus 502. Communication interface 518 provides a two-way datacommunication coupling to a network link 520 that is connected to alocal network 522. For example, communication interface 518 may be anintegrated services digital network (ISDN) card or a modem to provide adata communication connection to a corresponding type of telephone line.As another example, communication interface 518 may be a local areanetwork (LAN) card to provide a data communication connection to acompatible LAN. Wireless links may also be implemented. In any suchimplementation, communication interface 518 sends and receiveselectrical, electromagnetic or optical signals that carry digital datastreams representing various types of information.

Network link 520 typically provides data communication through one ormore networks to other data devices. For example, network link 520 mayprovide a connection through local network 522 to a host computer 524 orto data equipment operated by an Internet Service Provider (ISP) 526.ISP 526 in turn provides data communication services through the worldwide packet data communication network now commonly referred to as the“Internet” 528. Local network 522 and Internet 528 both use electrical,electromagnetic or optical signals that carry digital data streams. Thesignals through the various networks and the signals on network link 520and through communication interface 518, which carry the digital data toand from computer system 500, are exemplary forms of carrier wavestransporting the information.

Computer system 500 can send messages and receive data, includingprogram code, through the network(s), network link 520 and communicationinterface 518. In the Internet example, a server 530 might transmit arequested code for an application program through Internet 528, ISP 526,local network 522 and communication interface 518.

The received code may be executed by processor 504 as it is received,and/or stored in storage device 510, or other non-volatile storage forlater execution. In this manner, computer system 500 may obtainapplication code in the form of a carrier wave.

In the foregoing specification, embodiments of the invention have beendescribed with reference to numerous specific details that may vary fromimplementation to implementation. Thus, the sole and exclusive indicatorof what is the invention, and is intended by the applicants to be theinvention, is the set of claims that issue from this application, in thespecific form in which such claims issue, including any subsequentcorrection. Any definitions expressly set forth herein for termscontained in such claims shall govern the meaning of such terms as usedin the claims. Hence, no limitation, element, property, feature,advantage or attribute that is not expressly recited in a claim shouldlimit the scope of such claim in any way. The specification and drawingsare, accordingly, to be regarded in an illustrative rather than arestrictive sense.

1. A method comprising: receiving a first audio stream comprising one ormore channels of audio data; storing audio data of each channel of theone or more channels of the first audio stream in a separate section ofa first buffer comprising a plurality of corresponding sections;receiving a second audio stream comprising one or more channels of audiodata; storing audio data of each channel of the one or more channels ofthe second audio stream in a separate section of a second buffercomprising a plurality of corresponding sections; receiving a firstrequest from a client for audio data of at least one channel of thefirst audio stream; receiving a second request from the client for audiodata of at least one channel of the second audio stream; in response tothe first request, providing to the client audio data of the at leastone channel of the first audio stream from the corresponding section ofthe first buffer in which audio data of the at least one channel of thefirst audio stream is stored; and in response to the second request,providing to the client audio data of the at least one channel of thesecond audio stream from the corresponding section of the second bufferin which audio data of the at least one channel of the second audiostream is stored; wherein the method is performed by a computing device.2. The method according to claim 1, wherein the one or more channels ofaudio data of the first audio stream, when combined, constitute anoverall audio composition; and wherein the one or more channels of audiodata of the second audio stream, when combined, constitute an overallaudio composition.
 3. The method according to claim 1, wherein eachsection of the plurality of sections of the first buffer stores audiodata of only one channel of the one or more channel of the first audiostream; wherein audio data of each channel of the one or more channelsof the first audio stream is stored in only one section of the pluralityof sections of the first buffer; wherein each section of the pluralityof sections of the second buffer stores audio data of only one channelof the one or more channel of the second audio stream; wherein audiodata of each channel of the one or more channels of the second audiostream is stored in only one section of the plurality of sections of thesecond buffer.
 4. The method according to claim 1, wherein at least theone or more channels of audio data of the first audio stream areinterleaved, the method further comprising: prior to storing audio dataof each channel of the one or more channels of the first audio stream ina separate section of a first buffer, de-interleaving the one or morechannels of audio data of the first audio stream.
 5. The methodaccording to claim 1, wherein the first and second buffers are ringbuffers.
 6. The method according to claim 1, wherein the first audiostream comprises more than two channels of audio data, and whereinreceiving a first request from a client for audio data of at least onechannel of the first audio stream comprises receiving a first requestfrom a client for audio data of at least three channels of the firstaudio stream, the method further comprising: in response to the firstrequest, providing to the client, for each requested channel of the atleast three channels, audio data of the requested channel from thecorresponding section of the first buffer in which audio data of therequested channel is stored.
 7. The method according to claim 1, furthercomprising: receiving a plurality of requests from a plurality ofclients, wherein each request of the plurality of requests requestsaudio data of at least one channel of the one or more channels of thefirst audio stream; in response to each request of the plurality ofrequests, providing, to a client of the plurality of clients, audio dataof the at least one channel requested by the request from thecorresponding section of the first buffer in which audio data of theleast one channel requested by the request is stored.
 8. A methodcomprising: receiving an audio stream comprising more than two channelsof audio data; storing audio data of each channel of the more than twochannels in a separate section of a buffer comprising a plurality ofcorresponding sections; receiving a request from a client for at leastthree channels of the more than two channels of audio data; in responseto the request, providing to the client, for each requested channel ofthe at least three channels, audio data of the requested channel fromthe corresponding section of the buffer in which audio data of therequested channel is stored; wherein the method is performed by acomputing device.
 9. The method according to claim 8, wherein the morethan two channels of audio data, when combined, constitute an overallaudio composition;
 10. The method according to claim 8, wherein eachsection of the plurality of sections stores audio data of only onechannel of the more than two channels; and wherein audio data of eachchannel of the more than two channels is stored in only one section ofthe plurality of sections.
 11. The method according to claim 8, whereinthe more than two channels of audio data are interleaved, the methodfurther comprising: prior to storing audio data of each channel of themore than two channels in a separate section of a buffer,de-interleaving the more than two channels of audio data.
 12. The methodaccording to claim 8, wherein the buffer is a ring buffer.
 13. Themethod according to claim 8, further comprising: receiving another audiostream comprising one or more channels of audio data; storing audio dataof each channel of the one or more channels of the other audio stream ina separate section of another buffer comprising a plurality ofcorresponding sections; receiving another request from the client foraudio data of at least one channel of the other audio stream; and inresponse to the other request, providing to the client audio data of theat least one channel of the other audio stream from the correspondingsection of the other buffer in which audio data of the at least onechannel of the other audio stream is stored.
 14. The method according toclaim 8, further comprising: receiving a plurality of requests from aplurality of clients, wherein each request of the plurality of requestsrequests audio data of at least one channel of the more than twochannels; in response to each request of the plurality of requests,providing, to a client of the plurality of clients, audio data of the atleast one channel requested by the request from the correspondingsection of the buffer in which audio data of the least one channelrequested by the request is stored.
 15. A method comprising: receivingan audio stream comprising multiple channels of audio data; storingaudio data of each of the multiple channels in a separate section of abuffer comprising a plurality of corresponding sections; receiving aplurality of requests from a plurality of clients, wherein each requestrequests audio data of at least one channel of the multiple channels; inresponse to each request of the plurality of requests, providing, to aclient of the plurality of clients, audio data of the at least onechannel requested by the request from the corresponding section of thebuffer in which audio data of the least one channel requested by therequest is stored; wherein the method is performed by one or morecomputing devices.
 16. The method according to claim 15, wherein themultiple channels of audio data, when combined, constitute an overallaudio composition;
 17. The method according to claim 15, wherein eachsection of the plurality of sections stores audio data of only onechannel of the multiple channels; wherein audio data of each channel ofthe multiple channels is stored in only one section of the plurality ofsections.
 18. The method according to claim 15, wherein the multiplechannels of audio data are interleaved, the method further comprising:prior to storing audio data of each of the multiple channels in aseparate section of a buffer, de-interleaving the multiple channels ofaudio data.
 19. The method according to claim 15, wherein the buffer isa ring buffer.
 20. The method according to claim 15, wherein the audiostream comprises more than two channels of audio data, and whereinreceiving a plurality of requests from a plurality of clients comprisesreceiving a particular request from a particular client of the pluralityof clients for at least three channels of the more than two channels ofaudio data, the method further comprising: in response to the particularrequest, providing to the particular client, for each requested channelof the at least three channels, audio data of the requested channel fromthe corresponding section of the buffer in which audio data of therequested channel is stored.
 21. The method according to claim 1,further comprising: receiving another audio stream comprising one ormore channels of audio data; storing audio data of each channel of theone or more channels of the other audio stream in a separate section ofanother buffer comprising a plurality of corresponding sections;receiving a particular request from a particular client for audio dataof at least one channel of the other audio stream; and in response tothe particular request, providing to the particular client audio data ofthe at least one channel of the other audio stream from thecorresponding section of the other buffer in which audio data of the atleast one channel of the other audio stream is stored.
 22. Anon-transitory computer-readable medium storing processor-executableinstructions for performing the method of claim
 1. 23. A non-transitorycomputer-readable medium storing processor-executable instructions forperforming the method of claim
 8. 24. A non-transitory computer-readablemedium storing processor-executable instructions for performing themethod of claim 15.